A Concept for an Integrated R744 Heat Pump for Low-heating-energy Buildings

In low-heating-energy buildings heat pumps have become an attractive heating system due to a notable reduction of the space heating requirements and the introduction of low temperature heating systems. Comfort cooling becomes also more important, especially in lightweight buildings with large south-oriented windows, which partially tend to overheat in summer. A heat pump has the unique feature that heating and cooling can be provided with the same system and also at the same time. Thus, an integrated heat pump system with the functions heating, cooling and preparation of domestic hot water is an interesting solution for the energy supply of low-heating-energy buildings. In the first project phase different concepts for integrated heat pumps were investigated by means of simulations of the refrigerant cycles in the different operation modes using different refrigerants (R134a, R290, R744). Due to these results a brine/water heat pump system with the natural refrigerant R744 (CO2) was chosen for the further work. A prototype of this system is being constructed and will be tested at the Institute of Thermal Engineering. This paper briefly describes the investigated systems and the results of the simulation work and discusses the prototype system realized.